Mixed ionic conductor and device using the same

ABSTRACT

A mixed ionic conductor with an ion conductive oxide has a perovskite structure of the formula Ba a (Ce 1-b M 1   b )L c O 3-α , wherein
         M 1  is at least one trivalent rare earth element other than Ce;   L is at least one element selected from the group consisting of Zr, Ti, V, Nb, Cr, Mo, W, Fe, Co, Ni, Cu, Ag, Au, Pd, Pt, Bi, Sb, Sn, Pb and Ga;
 
with 0.9≦a≦1;
   0.16≦b≦0.26;   0.01≦c≦0.1;
 
and (2+b−2a)/2≦α&lt;1.5.
       

     Such a mixed ionic conductor has not only the necessary conductivity for electrochemical devices such as fuel cells, but also superior moisture resistance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mixed ionic conductor and anelectrochemical device, such as a fuel cell or a gas sensor, using thesame.

2. Description of the Prior Art

The applicant has long been actively developing mixed conductors ofprotons and oxide ions (see for example Publication of UnexaminedJapanese Patent Application (Tokkai) No. H5-28820 or H6-231611). Thesemixed ionic conductors are basically perovskite oxides containing bariumand cerium wherein a portion of the cerium has been substituted by thesubstitute element M, so as to achieve a high ionic conductivity(chemical formula: BaCe_(1−p)M_(p)O_(3−α)). Especially, when thesubstitution amount p of the substitution element M is 0.16 to 0.23, themixed ionic conductor has a high conductivity, higher even thanzirconia-based oxides (YSZ: yttrium-stabilized zirconia), whichconventionally have been used as oxide ionic conductors. As thesubstitution element M, rare earth elements are suitable, in particularheavy rare earth elements, because of their atomic radius and chargebalance.

New fuel cells, sensors and other electrochemical devices using suchmaterials as a solid electrolyte have been developed. The sensorcharacteristics and the discharge characteristics of fuel cells usingsuch materials have been shown to be superior to prior devices. Otherpatent applications related to these materials are Tokkai H5-234604,Tokkai H5-290860, Tokkai H6-223857, Tokkai H6-290802, Tokkai H7-65839,Tokkai H7-136455, Tokkai H8-29390, Tokkai H8-162121, and TokkaiH8-220060.

However, these materials show some problems with regard to theirchemical stability. For example, barium tends to precipitate in CO₂ gas.To solve these problems, the applicant has proposed a counter-strategyin Tokkai H9-295866. However, even this counter-strategy is not perfect,and for example at low temperatures of 85° C. and 85% humidity,precipitation can be observed in shelf tests and boiling tests in water.Moreover, under high water vapor pressures as during discharge of thefuel cells, barium can be seen to precipitate near the platinumelectrodes. Furthermore, with gas sensors, there is the problem ofmaintaining high ion conductivity at lower temperatures over a long timeand the problem of raising the acid resistance of the oxide itself.

SUMMARY OF THE INVENTION

To solve these problems, it is an object of the present invention toimprove the chemical stability of the mixed ionic conductors.

The main cause for decomposition of the oxides due to humidity isbelieved to be the fact that the segregated barium turning into bariumhydroxide reacts with the carbon dioxide, and forms stable bariumcarbonate. To increase the moisture resistance, the present inventionuses a mixed ionic conductor including the following perovskitestructure oxide.

A mixed ionic conductor of one embodiment of the present invention (afirst ionic conductor) includes an ion conductive oxide having aperovskite structure of the formula Ba_(a)(Ce_(1−b)M¹ _(b))L_(c)O_(3−α),wherein

-   -   M¹ is at least one trivalent rare earth element other than Ce;    -   L is at least one element selected from the group consisting of        Zr, Ti, V, Nb, Cr, Mo, W. Fe, Co, Ni, Cu, Ag, Au, Pd, Pt, Bi,        Sb, Sn, Pb and Ga;        with 0.9≦a≦1;    -   0.16≦b≦0.26;    -   0.01≦c≦0.1;        and (2+b−2a)/2≦α<1.5.

In this mixed ionic conductor it is preferable that M¹ is at least oneelement selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Y and Sc. More preferably, M¹ is Gd and/orY.

It is also preferable that L is at least one element selected from thegroup consisting of Zr, Ti, Fe, Co, Ni, Cu, Bi, Sn, Pb and Ga. Morepreferably, L is at least one element selected from the group consistingof Zr, Ti, Bi, Pb and Ga.

A mixed ionic conductor of another embodiment of the present invention(a second ionic conductor) includes an ion conductive oxide having aperovskite structure of the formula Ba_(e)Zr_(1−z)M² _(z)O_(3−β),wherein

-   -   0.9≦e≦1;    -   M² is at least one element selected from the group consisting of        trivalent rare earth elements, Bi, Ga, Sn, Sb and In;        with 0.01≦z≦0.3;        and (2+z−2e)/2≦β<1.5.

In this mixed ionic conductor it is preferable that 0.16≦z≦0.3. It isalso preferable that M² is at least one element selected from the groupconsisting of trivalent rare earth elements and In, especially elementsselected from the group consisting of Pr, Eu, Gd, Yb, Sc and In.

A mixed ionic conductor of yet another embodiment of the presentinvention (a third ionic conductor) includes an ion conductive oxidehaving a perovskite structure of the formula Ba_(d)Zr_(1−x−y)Ce_(x)M³_(y)O_(3−γ) wherein

-   -   M³ is at least one element selected from the group consisting of        trivalent rare earth elements, Bi and In;        with 0.98≦d≦1;    -   0.01≦x≦0.5;    -   0.01≦y≦0.3;        and (2+y−2d)/2≦γ<1.5.

In this third mixed ionic conductor, it is preferable that M³ is atleast one element selected from the group consisting of Nd, Sm, Eu, Gd,Tb, Yb, Y. Sc and In. More preferably, M³ is at least one elementselected from the group consisting of Gd, In, Y and Yb.

The mixed ionic conductors of the present invention have not only thenecessary conductivity for electrochemical devices such as fuel cells,but also superior moisture resistance.

Throughout this specification, “rare earth element” means Sc, Y, and thelanthanides (elements 57La through 71Lu). In the above formulas, α, βand γ are determined by the absent amount of disproportionate oxygen.

The present invention also provides devices using such a mixed ionicconductor. A fuel cell in accordance with the present invention includesas a solid-state electrolyte a mixed ionic conductor as described above.A gas sensor in accordance with the present invention includes as asolid-state electrolyte a mixed ionic conductor as described above.Using the mixed ionic conductors of the present invention provideselectric devices, such as fuel cells and gas sensors, with high moistureresistance, high performance, and long lifetimes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective cross-sectional view of an embodimentof a fuel cell using a mixed ionic conductor in accordance with thepresent invention.

FIG. 2 is a cross-sectional view of an embodiment of a gas sensor usinga mixed ionic conductor in accordance with the present invention.

FIG. 3 is a graph showing the conductivity of mixed ionic conductors inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is an explanation of the preferred embodiments of thepresent invention.

As the applicant has pointed out in the above-noted publications, thehigh conductivity of mixed ionic conductors in accordance with thepresent invention stems from the mixed ion conductivity of oxygen ionsand protons. In order to improve the moisture resistance of such mixedionic conductors, a suitable substitute element is introduced into theabove-mentioned first ionic conductor so as to reduce the amount ofbarium in the perovskite oxide to less than the stochiometric ratio. Inthe following, such a mixed ionic conductor also is referred to as“additive system” conductor.

The second and the third ionic conductors in accordance with the presentinvention are also mixed ionic conductors with high moisture resistance.In the following, these mixed ionic conductors are referred to as“barium-zirconium system” conductors and “barium zirconium ceriumsystem” conductors, respectively. While these systems are mixed ionicconductors exhibiting proton conductivity, they still provide highmoisture resistance.

These systems of mixed ionic conductors can be obtained withconventional raw materials and manufacturing methods. Specific examplesof manufacturing methods are explained along with the examples furtherbelow.

The following is an explanation of a device using a mixed ionicconductor in accordance with the present invention.

FIG. 1 is a cross-sectional perspective view of an embodiment of a fuelcell in accordance with the present invention. This planar fuel cell hasseveral layered units 7, which include a cathode (fuel electrode) 3, asolid electrolyte 2 layered on the cathode 3, and an anode (airelectrode) 1 on the solid electrolyte 2. Separators 4 are arrangedbetween the layered units 7.

When generating power, an oxidation gas 6 (such as air) is supplied tothe anodes 1, and a fuel gas 5 (a reduction gas such as hydrogen ornatural gas) is supplied to the cathodes 3. The oxidation-reductionreaction at the electrodes generates electrons, so that the fuel cellserves as an electric power source.

FIG. 2 is a cross-sectional view of an embodiment of a gas sensor inaccordance with the present invention. This HC sensor (hydrocarbonsensor) includes an anode 15, a solid electrolyte 14 on the anode 15,and a cathode 16 on the solid electrolyte 14. This layered structure isattached with an inorganic adhesive 18 to a (ceramic) substrate 17,providing a space 20 between the substrate and the layered structure.This space 20 is in communication with the outside via a diffusionlimiting hole 13.

When a certain voltage (for example 1.2V) is applied steadily betweenthe two electrodes 15 and 16, a current that is proportional to theconcentration of hydrocarbons in the space adjacent to the anode 15 isattained as output. During the measurement, the sensor is kept at acertain temperature with a heater 19 attached to the substrate. Toprovide the diffusion limiting hole 13 is advantageous to limit theinflow of the material to be measured (here, hydrocarbons) into thespace 20.

This embodiment has been explained for a HC sensor, but an oxygen sensoris also possible by exchanging anode and cathode in the structure shownin FIG. 2. Furthermore, the mixed ionic conductor of the presentinvention is not limited the above, but also can be applied to all kindsof other electrochemical devices.

EXAMPLES

The following is a more detailed description of specific examples of thepresent invention. It should be noted that the present invention is inno way limited to these examples.

As examples of the present invention, oxides as shown in Tables 1 to 6have been synthesized. These oxides were synthesized by solid statesintering. An oxide powder of barium, cerium, zirconium, and rare earthelements was weighed to the composition ratio listed in the tables, andcrushed and mixed with ethanol in an agate mortar. After sufficientmixing, the solvent was removed, defatted with a burner, and crushingand mixing were repeated in the agate mortar. Then, the samples werepressed into columnar shape and fired for 10 hours at 1300° C. After thefiring, granules of about 3 μm were produced by coarse crushing, withfurther crushing in a benzene solution with a planetary ball mill. Theresulting powder was vacuum-dried at 150° C., and columns were formedwith a hydrostatic press at 2 tons/cm², which were immediately fired for10 hours at 1650° C. to synthesize a sintered product. For almost allsamples, a very compact single-phase perovskite oxide was attained. Theresulting samples were then evaluated as follows:

Boiling Test

As an accelerated test of moisture resistance, the samples wereintroduced into boiling water of 100° C., and the level of Baprecipitation was evaluated after 10 hours by measuring the pH value.This evaluation utilizes the fact that the pH value in the aqueoussolution rises proportionally with the precipitation of barium. For a pHchange of not more than 2, the moisture resistance was taken to beexcellent (A), for more than 2 and not more than 3.5, it was taken to begood (B), for more than 3.5 and not more than. 4, it was taken to beadequate (C), and for more than 4, it was taken to be poor (D).

Conductivity

After the above-mentioned boiling test, disks of 0.5 mm thickness and 13mm diameter were made of the columnar sintered product samples, bothsides of the disks were coated with a platinum paste on an area of 0.5cm² each, which was baked onto the samples, and the ion conductivity wasmeasured. In this experiment, the conductivity was calculated from theresistance with the alternating current impedance method in air. Themeasurement temperature was 500° C. The resistance of the leads of themeasurement device was subtracted. When the conductivity (in S/cm) wasat least 0.007, it was taken as A, for at least 0.001 and less than0.007 it was taken as B, and for less than 0.001 it was taken as C.

FIG. 3 is an arrhenius plot showing the conductivity of materials inaccordance with the present invention.

Crystallinity

When the sintered product was single-phase it was taken as A, when itwas multi-phase, it was taken as B, and sintering failures were taken asC.

The tables show the conductivity at 500° C. and the result of the pHevaluation in the boiling test.

TABLE 1 Material Boiling Test Crystallinity ConductivityBaCe_(0.8)Gd_(0.2)O_(3−α) D A A Ba_(0.99)Ce_(0.8)Gd_(0.2)O_(3−α) D A ABa_(0.98)Ce_(0.8)Gd_(0.2)O_(3−α) D A A Ba_(0.94)Ce_(0.8)Gd_(0.2)O_(3−α)D A B Ba_(0.90)Ce_(0.8)Gd_(0.2)O_(3−α) D A B

TABLE 2 Additive System Material Boiling Test Crystallinity ConductivityBaCe_(0.8)Gd_(0.2)Zr_(0.01)O_(3−α) B A ABaCe_(0.8)Gd_(0.2)Zr_(0.04)O_(3−α) B A ABaCe_(0.8)Gd_(0.2)Zr_(0.06)O_(3−α) B A ABaCe_(0.8)Gd_(0.2)Zr_(0.1)O_(3−α) B A ABaCe_(0.8)Gd_(0.2)Zr_(0.11)O_(3−α) D B not measuredBaCe_(0.8)Gd_(0.2)Zr_(0.15)O_(3−α) D C not measuredBa_(0.99)Ce_(0.8)Gd_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.99)Ce_(0.8)Gd_(0.2)Zr_(0.04)O_(3−α) B A ABa_(0.99)Ce_(0.8)Gd_(0.2)Zr_(0.06)O_(3−α) B A BBa_(0.99)Ce_(0.8)Gd_(0.2)Zr_(0.1)O_(3−α) B A BBa_(0.99)Ce_(0.8)Gd_(0.2)Zr_(0.11)O_(3−α) B B CBa_(0.98)Ce_(0.8)Gd_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.98)Ce_(0.8)Gd_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)Zr_(0.06)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)Zr_(0.1)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)Zr_(0.11)O_(3−α) B B CBa_(0.98)Ce_(0.8)Gd_(0.16)Zr_(0.04)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.23)Zr_(0.04)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.26)Zr_(0.04)O_(3−α) B A ABa_(0.9)Ce_(0.8)Gd_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Gd_(0.2)Zr_(0.04)O_(3−α) B A CBa_(0.9)Ce_(0.8)Gd_(0.2)Zr_(0.06)O_(3−α) B A CBa_(0.9)Ce_(0.8)Gd_(0.2)Zr_(0.1)O_(3−α) A A CBa_(0.9)Ce_(0.8)Gd_(0.2)Zr_(0.11)O_(3−α) A B DBa_(0.89)Ce_(0.8)Gd_(0.2)Zr_(0.01)O_(3−α) B A CBa_(0.85)Ce_(0.8)Gd_(0.2)Zr_(0.04)O_(3−α) B A D

TABLE 3 Additive System Material Boiling Test Crystallinity ConductivityBa_(0.98)Ce_(0.8)Y_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Y_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Y_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)La_(0.2)Zr_(0.04)O_(3−α) B A CBa_(0.99)Ce_(0.8)La_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)La_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Pr_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Pr_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Pr_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Nd_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Nd_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Nd_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Pm_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Pm_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Pm_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Sm_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Sm_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Sm_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Eu_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Eu_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Eu_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Tb_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Tb_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Tb_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Dy_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Dy_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Dy_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Ho_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Ho_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Ho_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Er_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Er_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Er_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Tm_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Tm_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Tm_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Yb_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Yb_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Yb_(0.2)Zr_(0.1)O_(3−α) B A C

TABLE 4 Additive System Material Boiling Test Crystallinity ConductivityBa_(0.99)Ce_(0.8)Gd_(0.2)Ti_(0.01)O_(3−α) B A CBa_(0.99)Ce_(0.8)Gd_(0.2)Ti_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Ti_(0.04)O_(3−α) B A CBa_(0.9)Ce_(0.8)Gd_(0.2)Ti_(0.1)O_(3−α) A A CBa_(0.98)Ce_(0.8)Gd_(0.16)Ti_(0.04)O_(3−α) B A CBa_(0.99)Ce_(0.8)Gd_(0.2)Bi_(0.01)O_(3−α) B A ABa_(0.99)Ce_(0.8)Gd_(0.2)Bi_(0.1)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)Bi_(0.04)O_(3−α) B A BBa_(0.9)Ce_(0.8)Gd_(0.2)Bi_(0.1)O_(3−α) A A CBa_(0.98)Ce_(0.8)Gd_(0.16)Bi_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Gd_(0.2)Pb_(0.01)O_(3−α) B A BBa_(0.99)Ce_(0.8)Gd_(0.2)Pb_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Pb_(0.04)O_(3−α) B A CBa_(0.9)Ce_(0.8)Gd_(0.2)Pb_(0.1)O_(3−α) A A CBa_(0.98)Ce_(0.8)Gd_(0.16)Pb_(0.04)O_(3−α) B A CBa_(0.99)Ce_(0.8)Gd_(0.2)Ga_(0.01)O_(3−α) B A ABa_(0.99)Ce_(0.8)Gd_(0.2)Ga_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Ga_(0.04)O_(3−α) B A BBa_(0.9)Ce_(0.8)Gd_(0.2)Ga_(0.1)O_(3−α) A A CBa_(0.98)Ce_(0.8)Gd_(0.16)Ga_(0.04)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)V_(0.04)O_(3−α) C A CBa_(0.98)Ce_(0.8)Gd_(0.2)Nb_(0.04)O_(3−α) C A CBa_(0.98)Ce_(0.8)Gd_(0.2)Cr_(0.04)O_(3−α) C A CBa_(0.98)Ce_(0.8)Gd_(0.2)Mo_(0.04)O_(3−α) C A CBa_(0.98)Ce_(0.8)Gd_(0.2)W_(0.04)O_(3−α) C A CBa_(0.98)Ce_(0.8)Gd_(0.2)Fe_(0.04)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Co_(0.04)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Ni_(0.04)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Cu_(0.04)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)Ag_(0.04)O_(3−α) C A BBa_(0.98)Ce_(0.8)Gd_(0.2)Au_(0.04)O_(3−α) C A BBa_(0.98)Ce_(0.8)Gd_(0.2)Pd_(0.04)O_(3−α) C A BBa_(0.98)Ce_(0.8)Gd_(0.2)Pt_(0.04)O_(3−α) C A BBa_(0.98)Ce_(0.8)Gd_(0.2)Sb_(0.04)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Sn_(0.04)O_(3−α) B A C

TABLE 5 Barium-Zirconium System Material Boiling Test CrystallinityConductivity BaZr_(0.84)Y_(0.16)O_(3−α) A A C BaZr_(0.8)Y_(0.2)O_(3−α) AA C BaZr_(0.75)Y_(0.25)O_(3−α) A A C BaZr_(0.7)Y_(0.3)O_(3−α) A A BBaZr_(0.65)Y_(0.35)O_(3−α) B C not measured BaZr_(0.8)In_(0.2)O_(3−α) AA C BaZr_(0.7)In_(0.3)O_(3−α) A A B BaZr_(0.95)Gd_(0.05)O_(3−α) A A CBaZr_(0.84)Gd_(0.16)O_(3−α) A A C BaZr_(0.8)Gd_(0.2)O_(3−α) A A CBaZr_(0.75)Gd_(0.25)O_(3−α) A A C BaZr_(0.7)Gd_(0.3)O_(3−α) A A BBaZr_(0.65)Gd_(0.35)O_(3−α) B C not measured BaZr_(0.84)Sc_(0.16)O_(3−α)A A C BaZr_(0.7)Sc_(0.3)O_(3−α) A A B BaZr_(0.84)Bi_(0.16)O_(3−α) B A CBaZr_(0.8)Bi_(0.2)O_(3−α) A A C BaZr_(0.75)Bi_(0.25)O_(3−α) A A CBaZr_(0.7)Bi_(0.3)O_(3−α) A A C BaZr_(0.95)Yb_(0.06)O_(3−α) A A CBaZr_(0.84)Yb_(0.16)O_(3−α) A A C BaZr_(0.8)Yb_(0.2)O_(3−α) A A CBaZr_(0.75)Yb_(0.25)O_(3−α) A A C BaZr_(0.7)Yb_(0.3)O_(3−α) B A CBaZr_(0.84)Dy_(0.16)O_(3−α) B A B BaZr_(0.75)Dy_(0.25)O_(3−α) A A CBaZr_(0.99)La_(0.01)O_(3−α) A A C BaZr_(0.95)La_(0.05)O_(3−α) A A CBaZr_(0.84)La_(0.16)O_(3−α) A A C BaZr_(0.95)Pr_(0.05)O_(3−α) A A CBaZr_(0.84)Pr_(0.16)O_(3−α) A A C BaZr_(0.75)Pr_(0.25)O_(3−α) A A BBaZr_(0.9)Nd_(0.1)O_(3−α) A A C BaZr_(0.84)Nd_(0.16)O_(3−α) A A CBaZr_(0.9)Pm_(0.1)O_(3−α) A A C BaZr_(0.84)Pm_(0.16)O_(3−α) A A CBaZr_(0.84)Sm_(0.16)O_(3−α) A A C BaZr_(0.8)Sm_(0.2)O_(3−α) A A CBaZr_(0.9)Eu_(0.1)O_(3−α) A A C BaZr_(0.82)Eu_(0.18)O_(3−α) A A CBaZr_(0.8)Eu_(0.2)O_(3−α) A A B BaZr_(0.82)Tb_(0.18)O_(3−α) A A CBaZr_(0.8)Ho_(0.2)O_(3−α) A A C BaZr_(0.74)Er_(0.26)O_(3−α) A A CBaZr_(0.72)Tm_(0.28)O_(3−α) A A C BaZr_(0.8)Ga_(0.2)O_(3−α) A A CBaZr_(0.7)Ga_(0.3)O_(3−α) A A C BaZr_(0.8)Sn_(0.2)O_(3−α) A A CBaZr_(0.75)Sn_(0.25)O_(3−α) A A C BaZr_(0.72)Sb_(0.28)O_(3−α) A A C

TABLE 6 Barium Zirconium Cerium System Material Boiling TestCrystallinity Conductivity BaCe_(0.1)Zr_(0.74)Y_(0.16)O_(3−α) B A BBaCe_(0.2)Zr_(0.64)Y_(0.16)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)Y_(0.2)O_(3−α) B A ABaCe_(0.05)Zr_(0.9)Gd_(0.05)O_(3−α) A A CBaCe_(0.15)Zr_(0.65)Gd_(0.2)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)Gd_(0.2)O_(3−α) B A ABaCe_(0.5)Zr_(0.3)Gd_(0.2)O_(3−α) B A ABaCe_(0.2)Zr_(0.6)Gd_(0.2)O_(3−α) A A BBa_(0.99)Ce_(0.2)Zr_(0.6)Gd_(0.2)O_(3−α) A A BBaCe_(0.35)Zr_(0.5)Gd_(0.15)O_(3−α) A A ABa_(0.99)Ce_(0.35)Zr_(0.5)Gd_(0.15)O_(3−α) A A ABaCe_(0.4)Zr_(0.45)Gd_(0.15)O_(3−α) A A BBaCe_(0.4)Zr_(0.5)Gd_(0.1)O_(3−α) A A BBaCe_(0.01)Zr_(0.7)Gd_(0.29)O_(3−α) A A CBaCe_(0.05)Zr_(0.85)Gd_(0.1)O_(3−α) A A CBaCe_(0.2)Zr_(0.65)Sc_(0.05)O_(3−α) A A CBaCe_(0.05)Zr_(0.8)Sc_(0.15)O_(3−α) A A CBaCe_(0.05)Zr_(0.85)Bi_(0.1)O_(3−α) A A CBaCe_(0.2)Zr_(0.6)Bi_(0.2)O_(3−α) A A CBaCe_(0.4)Zr_(0.55)Bi_(0.05)O_(3−α) A A CBaCe_(0.05)Zr_(0.7)Bi_(0.25)O_(3−α) A A CBaCe_(0.05)Zr_(0.9)Yb_(0.05)O_(3−α) A A CBaCe_(0.2)Zr_(0.75)Yb_(0.05)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)Yb_(0.2)O_(3−α) B A ABaCe_(0.05)Zr_(0.7)Yb_(0.25)O_(3−α) A A CBaCe_(0.1)Zr_(0.6)Yb_(0.3)O_(3−α) A A CBaCe_(0.05)Zr_(0.8)Dy_(0.15)O_(3−α) A A CBaCe_(0.2)Zr_(0.7)Dy_(0.1)O_(3−α) A A CBaCe_(0.2)Zr_(0.75)La_(0.05)O_(3−α) A A CBaCe_(0.05)Zr_(0.85)La_(0.05)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)La_(0.2)O_(3−α) A A CBaCe_(0.2)Zr_(0.75)Pr_(0.05)O_(3−α) A A CBaCe_(0.4)Zr_(0.5)Pr_(0.1)O_(3−α) B A CBaCe_(0.2)Zr_(0.7)Nd_(0.1)O_(3−α) A A CBaCe_(0.4)Zr_(0.45)Nd_(0.05)O_(3−α) B A BBaCe_(0.4)Zr_(0.4)Nd_(0.2)O_(3−α) B A BBaCe_(0.4)Zr_(0.4)Pm_(0.2)O_(3−α) B A CBaCe_(0.4)Zr_(0.5)Pm_(0.1)O_(3−α) B A CBaCe_(0.4)Zr_(0.5)Sm_(0.1)O_(3−α) B A BBaCe_(0.1)Zr_(0.7)Sm_(0.2)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)Eu_(0.2)O_(3−α) B A BBaCe_(0.4)Zr_(0.5)Eu_(0.1)O_(3−α) B A CBaCe_(0.4)Zr_(0.4)Eu_(0.2)O_(3−α) B A CBaCe_(0.4)Zr_(0.55)Tb_(0.05)O_(3−α) B A CBaCe_(0.05)Zr_(0.8)Ho_(0.15)O_(3−α) A A CBaCe_(0.5)Zr_(0.4)Er_(0.1)O_(3−α) B A CBaCe_(0.5)Zr_(0.35)Tm_(0.15)O_(3−α) B A CBaCe_(0.4)Zr_(0.4)Ga_(0.2)O_(3−α) B A CBaCe_(0.05)Zr_(0.7)Ga_(0.25)O_(3−α) A A CBaCe_(0.1)Zr_(0.8)Sn_(0.1)O_(3−α) A A CBaCe_(0.05)Zr_(0.75)Sn_(0.2)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)Sb_(0.2)O_(3−α) B A CBaCe_(0.4)Zr_(0.4)In_(0.2)O_(3−α) B A ABa_(0.99)Ce_(0.4)Zr_(0.4)In_(0.2)O_(3−α) B A ABaCe_(0.2)Zr_(0.6)In_(0.2)O_(3−α) A A BBaCe_(0.3)Zr_(0.5)In_(0.2)O_(3−α) A A ABaCe_(0.4)Zr_(0.5)In_(0.1)O_(3−α) A A ABaCe_(0.5)Zr_(0.4)In_(0.1)O_(3−α) A A ABaCe_(0.5)Zr_(0.3)In_(0.2)O_(3−α) A A ABaCe_(0.6)Zr_(0.3)In_(0.1)O_(3−α) B A A

As becomes clear from this evaluation, mixed ionic conductors inaccordance with the present invention have considerably better moistureresistance, while the ion conductivity can be held at a practical level.

The above examples have been synthesized by solid state sintering, butthere is no limitation to this method, and the oxide also can besynthesized by coprecipitation, nitration, spray granulation or anyother suitable method. It is also possible to use film forming methodssuch as CVD or sputtering methods. It is also possible to use thermalspraying. There is no limitation to the shape of the oxide, and it canbe of any shape, including bulk shapes and films.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, all changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

1. A mixed ionic conductor comprising an ion conductive oxide having aperovskite structure of the formula Ba_(a)(Ce_(1-b)M¹ _(b))L_(c)O_(3-α),wherein M¹ is at least one trivalent rare earth element other than Ce; Lis at least one element selected from the group consisting of Zr, Ti, V,Nb, Cr, Mo, W, Fe, Co, Ni, Cu, Ag, Au, Pd, Pt, Sb, Sn, and Pb; with0.9≦a≦1; 0.16≦b≦0.26; 0.01≦c≦0.1; and (2+b−2a)/2≦α≦1.5.
 2. The mixedionic conductor of claim 1, wherein M¹ is at least one element selectedfrom the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Y and Sc.
 3. The mixed ionic conductor of claim 2, wherein M¹ isat least one element selected from the group consisting of Gd and Y. 4.The mixed ionic conductor of claim 1, wherein L is at least one elementselected from the group consisting of Zr, Ti, Fe, Co, Ni, Cu, Sn, andPb.
 5. A fuel cell comprising as a solid-state electrolyte a mixed ionicconductor of claim
 1. 6. A gas sensor comprising as a solid-stateelectrolyte a mixed ionic conductor of claim 1.